Gram positive infections make up ~50% of all acute lung injury cases with Streptococcus pneumonia infections accounting for 45% of all community-acquired pneumonia (CAP) cases. CAP is accompanied by extensive permeability edema, characterized by a disruption in endothelial barrier integrity. A major factor in the severity of CAP is the secretion of bacterial virulence factors predominantly pneumolysin (PLY) and family member listeriolysin-0 (LLO). These gram positive virulence factors make plasma membrane pores that cause a Ca2+-influx in various cell types, stimulate host PLC activity and as we have recently shown, activate protein kinase C alpha (PKCalpha). Previously we showed that inhibition of PKCalpha is barrier protective against these gram-positive virulence factors. Further, this is due, at least in part, to the ability of PKC alpha to increase production of reactive oxygen- and -nitrogen species associated. LLO induces eNOS uncoupling, enhances peroxynitrite generation, and causes an increase in RhoA and Rac 1 nitration resulting in activation of the former and inhibition of the latter. This project will focus on distinct mechanisms of eNOS uncoupling that we hypothesize occurs via the PKCalpha mediated phosphorylation of eNOS at Thr495 rather than through increased ADMA generation (see Project 1). From our previously published studies and new preliminary data, the overall hypothesis that we will test in this proposal is that inhibition of PKCalpha leads to the enhanced release of NO from eNOS which stimulates the S-nitrosylation of RhoA and Rac 1. This modification leads to RhoA inhibition and Rac1 activation and EC barrier protection. Specific Aim 1 will determine the mechanism by which PKCalpha mediates PLY/LLO driven eNOS uncoupling. Specific Aim 2 will determine if PKCalpha-mediated increases in NO signaling attenuate the endothelial barrier disruption induced by PLY and LLO and whether this occurs via the S-nitrosylation of RhoA and Rac1. This Aim will also identify the specific cytokine residues on RhoA and Rac1 that are nitrosylated. Specific Aim 3 will determine the relative effects of reducing PKCalpha activity and directly enhancing RhoA and Rac1 Snitrosylation in protecting the endothelial barrier during ALI in vivo.